FreeIPA, Zitadel.

Would like to see answers to this as well. I haven't found any comparable options yet

There is no all in one solution.

You have to solve the individual parts separately:

• User directory, login: keycloak, authentik
• Configuration management: Ansible, Puppet

The user config management part is not solved well in my mind. Puppet is probably the best because it can pull config whenever a client is online, whereas Ansible is push based.

On the other hand this software can manage absolutely everything, not limited by what GPs support.

Linux server config management on the other hand is way ahead of Windows. Also Linux installs so quickly, and the images can be so small, many companies don't even patch, they just boot a fresh image every week (immutable infrastructure).

The closest I've ever found to AD for Linux is FreeIPA, though there's also vastool for corporate environments if you want to use actual AD on Linux.